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Doppler vortography : detection and quantification of the vortices in the left ventricleMehregan, Forough 09 1900 (has links)
Nous proposons une nouvelle méthode pour quantifier la vorticité intracardiaque (vortographie Doppler), basée sur l’imagerie Doppler conventionnelle. Afin de caractériser les vortex, nous utilisons un indice dénommé « Blood Vortex Signature (BVS) » (Signature Tourbillonnaire Sanguine) obtenu par l’application d’un filtre par noyau basé sur la covariance. La validation de l’indice BVS mesuré par vortographie Doppler a été réalisée à partir de champs Doppler issus de simulations et d’expériences in vitro. Des résultats préliminaires obtenus chez des sujets sains et des patients atteints de complications cardiaques sont également présentés dans ce mémoire. Des corrélations significatives ont été observées entre la vorticité estimée par vortographie Doppler et la méthode de référence (in silico: r2 = 0.98, in vitro: r2 = 0.86). Nos résultats suggèrent que la vortographie Doppler est une technique d’échographie cardiaque prometteuse pour quantifier les vortex intracardiaques. Cet outil d’évaluation pourrait être aisément appliqué en routine clinique pour détecter la présence d’une insuffisance ventriculaire et évaluer la fonction diastolique par échocardiographie Doppler. / We propose a new method for quantification of intra-cardiac vorticity (Doppler vortography) based on conventional Doppler images. To characterize the vortices, an index called “blood vortex signature” (BVS) was obtained using a specific covariance-based kernel filter. The reliability of BVS measured by Doppler vortography was assessed in mock Doppler fields issued from simulations and in vitro experimentations. Some preliminary results issued from healthy subjects and patients with heart disease were also presented in this research project. Strong correlations were obtained between the Doppler vortography-derived and ground-truth vorticities (in silico: r2 = 0.98, in vitro: r2 = 0.86, in vivo: p = 0.004). Our results demonstrated that Doppler vortography is a potentially promising echocardiographic tool for quantification of intra-ventricular vortex flow. This technique can be easily implemented for routine checks to recognize ventricular insufficiency and abnormal blood patterns at early stages of heart failure to decrease the morbidity of cardiac disease.
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Local imaging of magnetic flux in superconducting thin filmsShapoval, Tetyana 04 March 2010 (has links) (PDF)
Local studies of magnetic flux line (vortex) distribution in superconducting thin films and
their pinning by natural and artificial defects have been performed using low-temperature
magnetic force microscopy (LT-MFM).
Taken a 100 nm thin NbN film as an example, the depinning of vortices from natural
defects under the influence of the force that the MFM tip exerts on the individual vortex was
visualized and the local pinning force was estimated. The good agreement of these results with
global transport measurements demonstrates that MFM is a powerful and reliable method to
probe the local variation of the pinning landscape. Furthermore, it was demonstrated that the
presence of an ordered array of 1-μm-sized ferromagnetic permalloy dots being in a magneticvortex
state underneath the Nb film significantly influences the natural pinning landscape of
the superconductor leading to commensurate pinning effects. This strong pinning exceeds the
repulsive interaction between the superconducting vortices and allows vortex clusters to be
located at each dot. Additionally, for industrially applicable YBa$_2$Cu$_3$O$_{7-\delta} thin films the main
question discussed was the possibility of a direct correlation between vortices and artificial
defects as well as vortex imaging on rough as-prepared thin films. Since the surface roughness
(droplets, precipitates) causes a severe problem to the scanning MFM tip, a nanoscale wedge
polishing technique that allows to overcome this problem was developed. Mounting the sample
under a defined small angle results in a smooth surface and a monotonic thickness reduction
of the film along the length of the sample. It provides a continuous insight from the film
surface down to the substrate with surface sensitive scanning techniques.
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Local imaging of magnetic flux in superconducting thin filmsShapoval, Tetyana 26 January 2010 (has links)
Local studies of magnetic flux line (vortex) distribution in superconducting thin films and
their pinning by natural and artificial defects have been performed using low-temperature
magnetic force microscopy (LT-MFM).
Taken a 100 nm thin NbN film as an example, the depinning of vortices from natural
defects under the influence of the force that the MFM tip exerts on the individual vortex was
visualized and the local pinning force was estimated. The good agreement of these results with
global transport measurements demonstrates that MFM is a powerful and reliable method to
probe the local variation of the pinning landscape. Furthermore, it was demonstrated that the
presence of an ordered array of 1-μm-sized ferromagnetic permalloy dots being in a magneticvortex
state underneath the Nb film significantly influences the natural pinning landscape of
the superconductor leading to commensurate pinning effects. This strong pinning exceeds the
repulsive interaction between the superconducting vortices and allows vortex clusters to be
located at each dot. Additionally, for industrially applicable YBa$_2$Cu$_3$O$_{7-\delta} thin films the main
question discussed was the possibility of a direct correlation between vortices and artificial
defects as well as vortex imaging on rough as-prepared thin films. Since the surface roughness
(droplets, precipitates) causes a severe problem to the scanning MFM tip, a nanoscale wedge
polishing technique that allows to overcome this problem was developed. Mounting the sample
under a defined small angle results in a smooth surface and a monotonic thickness reduction
of the film along the length of the sample. It provides a continuous insight from the film
surface down to the substrate with surface sensitive scanning techniques.
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